Investigating methods to improve the reproductive performance of hoggets : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
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Date
2011
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Massey University
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Abstract
The first two chapters identified that in comparison to mature multiparous ewes, fewer
hoggets are bred, a greater proportion return to oestrus, have a lower proportion that ovulate
and of those that do ovulate, the ovulation rate is lower, and there is a greater reproductive
loss in early to mid pregnancy, fewer and lighter singleton counterparts lambs at birth, poorer
mothering ability and lighter and fewer lambs at weaning.
As a result of these findings, nutritional management experiments were designed to
investigate the effects of nutrition on the reproductive performance of hoggets. The results
indicate that offering ad-libitum levels of herbage prior to ram introduction can increase the
proportion of hoggets bred which leads to a better pregnancy rate. However, ad-libitum levels
herbage immediately after the completion of the breeding period could be associated with
hoggets that were bred returning to oestrus. The efficiency of lamb production was reduced
when the hoggets were offered ad-libitum levels of herbage during pregnancy. However.
when twin-bearing hoggets were offered ad-libitum levels of nutrition from mid- to late- pregnancy
the efficiency of lamb production was similar between nutritional levels. The
twin-bearing hoggets may have both been offered a level of nutrition that did not lead to a
sufficient nutritional intake restriction in the medium group to allow for hogget live weight
differences to occur. Hoggets that were offered ad-libitum levels of nutrition during
pregnancy were heavier than the hoggets offered medium levels of nutrition. Weaning single
lambs born to hoggets at 10 weeks of age whilst weaning twin lambs at 9 weeks of age did
not have an impact on hogget or lamb live weight compared to weaning at 13 or 14 weeks of
age.
This thesis has identified reproductive differences between hoggets and mature multiparous
ewes and the impact of nutritional management on hogget reproductive performance and the
effect of weaning age on lamb and hogget live weight. Implementing the results from the
nutritional experiments into farm practice could improve hogget reproductive performance
and help alleviate the issue of the negative impact of hogget breeding on subsequent breeding
live weight, while also offering options to the farmer when planning the management of
weaning lambs born to hoggets.
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Keywords
Sheep, Reproduction, Ewes, Nutrition, Lambing, Hoggets, New Zealand